Separation of rare earth elements from other elements

Abstract

A process for separating rare earth elements (REE) from Ca, Mg and other non-REE elements comprises raising the pH of an acidic aqueous solution of REE to pH 8 to pH 11; adding nano- or micro (NoM) particles having a silica or titanium oxide surface; agitating the suspension for 6 h to 48 h to provide for adherent crystallization of REE hydroxide on the particles; separating the particles from the solution; releasing REE by treatment with aqueous acid to form an aqueous solution of REE salt; separating them from the aqueous solution of REE salt formed. The acidic aqueous solution comprising REE is preferably provided by leaching of an REE mineral with aqueous acid; adding a base to bring the pH to from pH 4.0 to pH 6.5; separating precipitated non-REE hydroxide from the solution.

The invention claimed is: 
     
       1. A process for separation of rare earth elements (REE) from calcium and magnesium, characterized in that the process comprises the following steps:
 a) providing an acidic aqueous solution of REE, calcium and magnesium; 
 b) adding a base to bring the pH of the solution to a pH in the range of pH 8 to pH 11, to form REE hydroxide; 
 c) adding nano- or micro- particles selected from silica particles, titanium oxide particles and particles covered by a layer of silica to the solution to provide a particle suspension; 
 d) agitating the particle suspension for a time period of from 6 h to 48 h, to provide for adherent crystallization of REE hydroxide on the particles; 
 e) separating the particles loaded with REE hydroxide from the aqueous solution; 
 f) releasing REE from the particles by treatment with aqueous acid to form an aqueous solution of REE salt; 
 g) separating the non-loaded particles from the aqueous solution of REE salt; 
 with the proviso that step c) can precede step b). 
 
     
     
       2. The process of  claim 1 , wherein the process is carried out at ambient temperature. 
     
     
       3. The process of  claim 1 , wherein particles covered with silica are iron(III) oxide particles. 
     
     
       4. The process of  claim 1 , wherein particles loaded with REE hydroxide are separated from the aqueous solution by filtration, decantation, centrifugation or by magnetic means. 
     
     
       5. The process of  claim 1 , wherein the base is selected from ammonia, sodium hydroxide, potassium hydroxide. 
     
     
       6. The process of  claim 5 , wherein the base is provided in form of an aqueous solution. 
     
     
       7. The process of  claim 1 , wherein the thickness of the silica layer is 10 μm or more. 
     
     
       8. The process of  claim 1 , wherein non-loaded particles are separated in step g) from the aqueous solution of REE salt by filtration, decantation, centrifugation or by magnetic means. 
     
     
       9. The process of  claim 1 , wherein treatment with aqueous acid is carried out at pH 2 or lower. 
     
     
       10. The process of  claim 1 , wherein the aqueous acid is selected from the group consisting of nitric acid, hydrochloric acid, hydrobromic acid. 
     
     
       11. The process of  claim 1 , wherein the acidic aqueous solution of REE, calcium and magnesium of step a) is provided by:
 i) leaching a mineral comprising REE with aqueous acid at pH 2 or lower to form an acidic solution comprising REE, magnesium, calcium, iron(III); 
 ii) adding a base to bring the pH of the leaching solution to a pH of from 4.0 to 6.5; 
 iii) separating precipitated iron(III) hydroxide by means of filtration, decantation or centrifugation so as to obtain said aqueous solution of REE, calcium and magnesium of step a). 
 
     
     
       12. The process of  claim 11 , wherein the base of step ii) is selected from ammonia, sodium hydroxide, potassium hydroxide. 
     
     
       13. The process of  claim 1 , wherein REE is selected from the group consisting of lanthanum, dysprosium, neodymium. 
     
     
       14. The process of  claim 1 , wherein the particles have a diameter of 5 nm to 100 μm. 
     
     
       15. The process of  claim 1 , wherein pH of the aqueous solution provided in step a) is continuously monitored. 
     
     
       16. The process of  claim 11 , wherein pH of the acid solution provided in step i) is continuously monitored. 
     
     
       17. The process of  claim 1 , wherein the base is provided in form of an aqueous solution thereof. 
     
     
       18. The process of  claim 11 , wherein the base of step ii) is provided in form of an aqueous solution thereof. 
     
     
       19. The process of  claim 1 , wherein step (b) comprises adding a base to bring the pH of the solution to a pH in the range of pH 9 to pH 10. 
     
     
       20. The process of  claim 1 , wherein the agitating of (d) is done for 12 h to 36 h.